Solar and infrared upwelling and downwelling radiation
10 Mar 2011



Incoming solar and infrared broadband radiation are measured using radiometers.


​Solar tracker with pyranometer and pyrheliometer


A wide range of solar and infrared broadband radiation measurements are made at Chilbolton Observatory. The properties of this broadband radiation at the earth's surface provide a wealth of information on atmospheric conditions above the site.

Broadband radiation is commonly measured in 2 wavelength bands:

  • A shorter wavelength band measuring radiation received from the sun. It encompasses the visible spectrum, together with near infrared and longer wavelength ultraviolet. This encompasses a wavelength range of approximately 0.29 - 2.8 µm. It shows a clear response to the day/night cycle. Clouds and other aerosols reduce the detected radiation.
  • A longer wavelength band encompassing longer wavelength infrared radiation (approximately 4.5 - 32 µm) produced by emission from the atmosphere and earth's surface. It does not respond significantly to the day/night cycle but changes according to the time of year and degree of cloud cover.
We also have further options for the type of broadband radiation measurement:
  • Radiation can be measured in both downwelling (from the sky) and upwelling (from the ground) configurations. The combination of these measurements gives information on the energy balance (which results in warming or cooling) at the earth's surface.
  • As well as measuring the total shorter wavelength radiation from across the sky, the measurement can be split to measure the radiation coming only from the sun (direct solar radiation) and the radiation coming from the remainder of the sky (diffuse solar radiation). The ratio of these measurements gives information on the scattering of solar radiation by clouds and other aerorosols (fog, dust, pollution etc.) in the atmosphere. To make these measurements, instruments are mounted on an automated solar tracker which correctly points the direct measurement instrument at the sun and shades the diffuse measurement instrument from the sun.

Net flux radiometer  
Net flux radiometer (showing upwelling sensors)

Summary of Chilbolton Observatory solar and infrared radiation measurements

Wavelength range Up/down welling
Sky contribution Instrument type
Instrument model
Down Total Pyranometer
CM21, CNR4
Short Down
Diffuse Shaded pyranometer
Short Down Direct Pyrheliometer

Note: the CNR4 is a net flux radiometer incorporating 4 sensors to measure both wavelength ranges in up and downwelling configurations. All other instruments make single measurements. All instruments are manufactured by Kipp & Zonen.

Technical specifications of the broadband radiometers
Contact: Jeffery, Judith (STFC,RAL,RALSP)